SERVICE MANUALROBERT BOSCH MODEL MW INJECTION PUMPSection 11After the specified plunger lift to port closure isestablished for number one barrel and plunger, theremaining barrels and plungers are "phased" indischarge order "port close" every sixty degrees.Fuel is retained around the barrel and within the pumphousing by an "O" ring and oval "O" ring. Located on thebarrel body and approximately three-eighths inchesbelow the barrel flange is an "O" ring groove. Thisgroove contains an oval "O" ring which seals against theupper housing bore and retains fuel within the upperhousing barrel cavity. An "O" ring located at the bottomof the injection pump housing cavity and retained by aspacer seals against the lower end of the barrel. Thespacer is pressed into the housing and can be replaced ifit is damaged.Barrel ConstructionWhen the barrel is installed into the pump housing, thebarrel flange with the adjustment notch is positionedopposite the control rack. Pump balance, which is theterm used to describe equal delivery per cylinder, isadjusted during production pump calibration by rotatingthe barrel using the adjustment notch (Figure 11).Figure 11. - Barrel ConstructionTwo fuel passages in the barrel allow fuel to flow fromthe pump housing cavity and into/ out of the plungerbarrel. The upper barrel passage is the charging andhigh pressure spill port and the lower passage is theleakoff port. The leakoff port indexes with a groove onthe plunger and allows high pressure fuel which hasleaked past the upper plunger/barrel to return to thepump housing cavity.To protect the pump housing from erosion when highpressure fuel spills back into the pump cavity at the endof the pumping cycle, a metal impact cap and retainingring covers the upper barrel duct. This cap has six holesand is installed so the holes do not align with thecharging port in the barrel.Plunger ConstructionEach barrel and plunger is a matched metal to metal fitto each other and produces peak injection pressure ofapproximately 9000 pounds per square inch. Camshaftrotation causes the roller tappet to lift the plunger aconstant amount or stroke on each pumping cycle. Fueldelivery per stroke is varied by rotating the plungerthrough a control sleeve, common control rack,governor and control lever to change the effectiveplunger stroke.At the top of the plunger, a retard start notch inconjunction with the charging/high pressure spill port inthe barrel aid engine starting by retarding injection timing(Figure 12). After the engine starts, effective plungerstroke is determined by the relationships between theplunger helix and the charging/high pressure spill port.The accelerator pedal must be fully depressed to allowthe control rack to move into the start fuel position.High pressure fuel that leaks past the upper plunger andbarrel area is returned to the pump housing cavitythrough the plunger leakoff groove and leakoff port in thebarrel. Additional smaller grooves located above theleakoff groove and 180 degrees from the helix allow fuelto flow to the leakoff groove.CGES-185-3PRINTED IN UNITED STATES OF AMERICAPage 10
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
